Preheat the oven to 400 degrees F. Put the sweet potatoes in a microwave-safe bowl with 2 tablespoons water. Cover loosely with plastic wrap and microwave until fork-tender, 10 minutes. Combine the sugar and 1 teaspoon each paprika and salt; rub on the steak. Let sit 5 minutes.
Heat 1 tablespoon olive oil in a large cast-iron skillet over medium-high heat. Add the steak and sear until browned, about 3 minutes per side. Transfer the skillet to the oven; cook 7 more minutes for medium rare. Transfer the steak to a cutting board and let rest 5 minutes before slicing. Return the skillet to medium-high heat. Add the jalapeno brine and scrape up any browned bits. Stir in the butter; set aside.
Meanwhile, heat a separate large skillet over medium-high heat. Add the remaining 2 tablespoons olive oil, the sweet potatoes, bell pepper, the remaining 1 teaspoon smoked paprika and 1/2 teaspoon salt. Cook, stirring, until the sweet potatoes are browned, about 5 minutes. Add the jalapenos, scallions and parsley and cook 2 more minutes. Serve with the steak and reserved pan sauce.